In combinatorial synthesis, it is often desirable to be able to distribute beads into a two-dimensional array, so that each variant in a combinatorial library can be identified by its position in the array. The array can consist of a set of plates, each having rows and columns of wells, with one bead, or some other predetermined number of beads, in each well. The beads are typically made of polystyrene, and serve as substrates for different compounds produced in the process of split and combine synthesis. Ultimately, the synthesized compounds are stripped from the beads and tested for activity. The identity of an active compound is determined by spectrographic analysis, in the light of the information available concerning the reaction histories of the beads being distributed.
The beads are spherical and of extremely small size, e.g. 300 mm in diameter. Consequently, they are difficult to handle, and it has been very difficult to separate a single bead from a mixture of beads.